title: Repair of chromosome damage induced by X-irradiation during G2 phase in a line of normal human fibroblasts and its malignant derivative.
abstract: A line of normal human skin fibroblasts (KD) differed from its malignant derivative (HUT-14) in the extent of cytogenetic damage induced by X-irradiation during G2 phase. Malignant cells had significantly more chromatid breaks and gaps after exposure to 25, 50, or 100 rad. On the assumption that each chromatid contains a single continuous DNA double helix, chromatid breaks would represent unrepaired DNA double-strand breaks; the gaps may represent single-strand breaks. Results from alkaline elution of cellular DNA immediately after irradiation showed that the normal and malignant cells in asynchronous population were equally sensitive to DNA single-strand breakage by X-irradiation. Caffeine or beta-cytosine arabinoside (ara-C), inhibitors of DNA repair, when added directly following G2 phase exposure, significantly increased the incidence of radiation-induced chromatid damage in the normal cells. In contrast, similar treatment of the malignant cells had little influence. Ara-C differed from caffeine in its effects; whereas both agents increased the frequency of chromatid breaks and gaps, only ara-C increased the frequency of gaps to the level observed in the irradiated malignant cells. Addition of catalase, which destroys H2O2, or mannitol, a scavenger of the derivative free hydroxyl radical (.OH), to the cultures of malignant cells before, during, and following irradiation significantly reduced the chromatid damage; and catalase prevented formation of chromatid gaps. The DNA damage induced by X-ray during G2 phase in the normal KD cells was apparently repaired by a caffeine- and ara-C-sensitive mechanism(s) that was deficient or absent in their malignant derivatives.
mesh_terms: D015112:4-Nitroquinoline-1-oxide; D002110:Caffeine / Q000494:pharmacology; D002374:Catalase / Q000494:pharmacology; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D002869:Chromosome Aberrations; D003561:Cytarabine / Q000494:pharmacology; D004260:DNA Repair / Q000187:drug effects*; D005347:Fibroblasts / Q000648:ultrastructure; D006801:Humans; D007399:Interphase / Q000528:radiation effects*; D008353:Mannitol / Q000494:pharmacology; D011829:Radiation Dosage
chemical_list: D003561:Cytarabine; D002110:Caffeine; D008353:Mannitol; D015112:4-Nitroquinoline-1-oxide; D002374:Catalase